There is significant market need and technical interest in finding ways to communicate voice information and call signaling information over existing data networks. An example application in this field is sending telephone calls, including both the voices of the calling parties and call set-up, tear-down, and related signaling information, over a packet-switched data network. There is particular interest in providing telephone call capability over the global, packet-switched public data network known as the Internet. A key motivation for this technology is that voice calls carried over the Internet do not incur telephone call toll charges, which are imposed by long-distance carriers and certain local telephone call carriers in the public switched telephone network. In short, voice-over-Internet technology may offer callers the ability to place low-cost calls over open protocol networks.
A significant leap forward in this field has been taken by the introduction of protocol conversion and signaling connection systems. An example of such a system is the Cisco SC2200 Signaling Converter, commercially available from Cisco Systems, Inc. Other examples of such a system are described in U.S. patent application Ser. No. 08/904,295 entitled “Universal Protocol Conversion,” filed on Jul. 31, 1997 by Lev Volftsun, et al., the entire contents of which are hereby incorporated by reference as if fully set forth herein.
Generally, such protocol conversion systems are implemented by a highly specialized computer system that interfaces to the data network and the public switched telephone network. The computer system executes one or more signaling protocol software applications to carry out the function of the system. The computer system may include one or more gateways that pass data signals to the telephone network and a media gateway controller that controls the gateways under control of a processor in the computer system.
One or more protocol converters may be configured, by running appropriate application software, as call processing devices or as signaling terminal devices. In some configurations, a call processing device is located logically remote from a signaling terminal device, coupled to it by an Internet Protocol (IP) network. In this configuration, there is a need to send telephone call signaling information, formatted according to standard telephony protocols, from a signaling terminal device back across the IP network to a call processing device. This is referred to as “backhauling” the signaling information.
As voice-over-Internet systems become more popular, it is necessary to support a larger number of channels from the gateway. It is difficult, however, to scale call processing devices to handle an increasing number of channels from the gateways. For example, a call processing device may manage a separate IP connection for every channel supported by each of the gateways.
Another difficulty in scalability is due to the capability of some gateways of supporting multiple signaling protocols over the same channel. One approach for handling such gateways is to provide an IP connection, not only for every channel on the gateway, but for every pair of channel and supported signaling protocols. For example, a gateway that supports 24 channels and 2 protocols would require 48 separate IP connections.
The performance in managing a separate IP connection for every channel or channel-protocol pair, however, tends to degrade after a certain number of IP connections, because the number of file descriptors and other operating system resources are limited. For example, some UNIX™ operating systems only allow up to 256 file descriptors, which translates to only about 250 supportable IP connections. When a call processing device is overloaded, a second call processing device would need to be purchased, often at a considerable cost.